Pressure compensation valve

ABSTRACT

A pressure compensation valve comprises a check valve portion having an inlet port that is connected to a discharge path of a hydraulic pump, an outlet port that is connected to an inlet side of a directional control valve, and a valve for controlling an area of opening between both ports. A pressure reduction valve portion has a spool that defines at its both sides a first pressure chamber and a second pressure chamber, respectively, and is adapted to be slidable to allow the valve to be thrusted in a first direction in which the area of opening is increased under a self-load pressure applied to the first pressure chamber and to be slidable to allow the valve to be thrusted in a second direction in which the area of opening is decreased under a pressure within the second pressure chamber. An internal passage is formed inside of the spool and is adapted to supply a discharge pressure fluid of the hydraulic pump to the second pressure chamber when the spool has been slid to assume not less than a predetermined displacement made in the first direction.

TECHNICAL FIELD

The present invention relates to a pressure compensation valve for usein a hydraulic circuit, e. g. a hydraulic circuit for supplying adischarge pressure fluid from one or more hydraulic pumps to a pluralityof actuators in distributed flow rates in a construction machine.

BACKGROUND ART

If it is attempted to supply a discharge pressure fluid from a hydraulicpump to a plurality of actuators, it has generally been known that thepressure fluid tends to be admitted only to an actuator of the lowestload pressure. In order to resolve this problem, it has been known tomake use of a certain hydraulic circuit, for example, as disclosed inJapanese Unexamined Patent Publication No. Sho 60-11706. In such ahydraulic circuit, a pressure compensation valve is provided,respectively, at the inlet side of a directional control valve that isarranged for each of the actuators. More specifically, this is ahydraulic circuit in which each of the pressure compensation valves isset for the highest of different load pressures which are met by therespective actuators so that a plurality of actuators of the varyingload pressures may be fed with a discharge pressure pressure withdistributed flow rates.

An example of the pressure compensation valve which can be used in sucha hydraulic circuit has been known that is disclosed, for example, inJapanese Unexamined Patent Publication No. Hei 4-244605.

This is a pressure compensating valve in which as shown in FIG. 1 of thedrawings attached hereto, a valve body 1 includes a check valve portion5 that is provided with a check valve bore la having an inlet port 2 andan outlet port 3, the said check valve bore la having a valve 4 slidablyfitted therein for establishing and blocking a communication between theinlet port 2 and the outlet port 3. The above mentioned valve body 1also includes a pressure reduction valve portion 12 that is providedwith a pressure reduction valve bore 1b having a first port 6, a secondport 8 and a third port 9, the said pressure reduction valve bore 1bhaving a spool 11 slidably fitted therein and having at its two ends,respectively, a first pressure chamber 7 that communicates with thefirst port 6 and a second pressure chamber 10 that communicates with thethird port 9 and in which under a pressure in the first pressure chamber7 the above mentioned spool 11 is thrusted rightwards for establishing acommunication between the second port 8 and the third port 9, and undera pressure in the second chamber 10 the said spool 11 is thrustedleftwards for blocking the communication between the second port 8 andthe third port 9. At this point it should be noted that the abovementioned spool 11 is designed to be thrusted by a spring 13 in such adirection as to block the communication between the second port 8 andthe third port 9 and then for abutment on the above mentioned valve 4.And, the said pressure compensation valve is constituted of thesecomponents.

If such a pressure compensation valve is adopted, it can be seen thatwhen a pressure within the first pressure chamber 7 is higher than apressure within the second pressure chamber 10, the said spool 11 willbe displaced rightwards to depart from the valve 4 and to position thevalve 4 so as to make a pressure in the inlet port 2 equal to a pressurein the outlet port 3. As a result, it can also be seen that a pressurewithin the first pressure chamber 7 and a pressure within the secondpressure chamber 10 will be made equal to each other. On the other hand,it can be noted that when a pressure within the first pressure chamber 7is lower than a pressure within the second pressure chamber 10, thevalve 4 will be thrusted with the spool 11 into its blocking position sothat the pressure in the outlet port 3 may be made lower than thepressure in the inlet port 2 by a pressure difference between the secondpressure chamber 10 and the first pressure chamber 7.

This being the case, it can be seen that by connecting the outlet port 3to a pump port 15 of a directional control valve 14, connecting thefirst port 6 to an outlet port 16 of the directional control valve 14 tointroduce a self-load pressure PI into the first pressure chamber 7,connecting the third port 9 to a load pressure detecting passage 17 tointroduce a control pressure P_(LS) into the second pressure chamber 10and connecting a discharge outlet 19 of a hydraulic pump 18 to the inletport 2 and the second port 8, the pump discharge pressure P₀ will becapable of being reduced by the differential pressure (P_(LS) -P₁) whichis the control pressure P_(LS) minus the self-load pressure P₁, to yieldan output pressure that is furnished at the outlet port 3.

For example, if P₀ is 120 kg/cm² and P_(LS) and P₁ are each 100 kg/cm²,the output pressure P₂ will be 120 kg/cm². Also, if P₀ is 120 kg/cm², P₁is 10 kg/cm² and P_(LS) is 100 kg/cm², the output pressure P₂ will be 30kg/cm².

By the way, it should be noted that such pressure compensation valveswill, for example, as shown in FIG. 2 of the drawings attached hereto,be disposed at the inlet sides of a plurality of directional controlvalves 14, respectively, provided in the discharge path 19 of thehydraulic pump 18 so that the respective third ports 14 of all thepressure compensation valves may communicate with the load pressuredetecting path 17 and that the respective second pressure chambers 10 ofall the pressure compensation valves may have acted thereon theself-load pressure P₁ of all the pressure compensation valves, that is,the highest of the different load pressures of all of actuators 20. Atthis point, it will be apparent in FIG. 2 that the pressure compensationvalves are each schematically shown.

In FIG. 2, there are also shown a swash plate 22 for controlling theflow rate of the discharge fluid of the hydraulic pump 18, a servocylinder 23 and a pump swash plate angle control valve 24. The said pumpswash plate angle control valve 24 is designed to be switchinglyoperated in response to a pressure difference between the pump dischargepressure P₀ and the load pressure P_(LS) to apply the pump dischargepressure P₀ to the servo cylinder 23, thereby altering the angle of theswash plate 25 so as to function to maintain the pressure differencebetween the pump discharge pressure P₀ and the load pressure P_(LS)always constant. At this point it should be noted that the load pressuredetecting path 17 is connected via a throttle 25 to a reservoir 26.

In the hydraulic circuit of FIG. 2, however, where the plurality of thedirectional control valves 14 are operated simultaneously to operate allthe actuators 20 concurrently, it will be noted that if a singleactuator 20 is assumed to have taken its displacement end position, thefact that there is no pressure fluid that flows between the inlet andoutlet ports should bring about the situation in which the dischargefluid pressure P₀ of the hydraulic pump 18 is rising to the set pressurefor a main relief valve 21. As a consequence, the load pressure P₁ ofthat actuator 20 which has taken the displacement end position will bemade equal to the pump discharge pressure P₀ and the load pressureP_(LS) will be made equal to the pump discharge pressure P₀, too. Thus,since the spool 11 is displaced rightwards so that the second port 8 andthe third port 9 may communicate with each other, the load pressureP_(LS) will be made equal to the pump discharge pressure P₀.

For this reason, the above mentioned set pressure for the said mainrelief valve 21 will act on the second chamber 10 of the pressurecompensation valve that is connected to another actuator 20 which hasnot reached its displacement end. And, since its first pressure chamber7 has acted thereon the self-load pressure P₁ that is lower than thesaid set pressure for the main relief valve 21, the spool 11 will act tothrust the valve 4 of the check valve portion 5 in the direction inwhich a communication between the inlet port 2 and the outlet port 3 canbe blocked. As a result, with the communication between the inlet port 2and the outlet port 3 blocked, there will be no pressure fluid forsupply to that actuator 20 which has not yet reached its displacementend and which will therefore is brought to a halt.

Accordingly, with the above mentioned problems in the prior art takeninto account, it is an object of the present invention to provide apressure compensation valve whereby in a hydraulic circuit for feeding adischarge pressure fluid from a single hydraulic pump to a plurality ofactuators in distributed flow rates where all of the plurality of theactuators are simultaneously operated by concurrently operating the likeplurality of directional control valves, even if a certain actuator hastaken its displacement end position, there can be no stoppage of anyother actuator.

SUMMARY OF THE INVENTION

In order to achieve the object mentioned above, there is provided inaccordance with the present invention, a pressure compensation valve,characterized in that it comprises:

a check valve portion having an inlet port that is connected to adischarge path of a hydraulic pump, an outlet port that is connected toan inlet side of a directional control valve and a valve for controllingan area of opening between both said ports; and

a pressure reduction valve portion which is comprised of a spool thatdefines at its both sides a first pressure chamber and a second pressurechamber, respectively, and is adapted to be slidable to allow the saidvalve to be thrusted in a first direction in which the said area ofopening is increased under a self-load pressure applied to the saidfirst pressure chamber and to be slidable to allow the said valve to bethrusted in a second direction in which the said area of opening isdecreased under a pressure within the said second pressure chamber, aninternal passage that is formed inside of the said spool and that isadapted to supply a discharge pressure fluid of the said hydraulic pumpto the said second pressure chamber when the said spool has been slid toassume not less than a predetermined displacement made in the said firstdirection, a first throttle that is disposed in the said internalpassage, and a port for establishing a communication between a loadpressure detecting path that is connected via a second throttle to areservoir and the said first throttle.

According to the construction mentioned above, since the pressure fluidwithin the said second pressure chamber is allowed to flow through thesaid throttle into the said load pressure detecting path and a portionof the said pressure fluid is allowed to flow via the said throttle ofthe load pressure detecting path into the said reservoir, it can be seenthat there will develop a constant flow and that there will also developa pressure difference behind and ahead of the said throttle and that asa result, a load pressure of the said load pressure detecting path willbe lower than a pressure within the said second pressure chamber.

Accordingly, in case where a pressure compensation valve is disposed,respectively, at the inlet side of each of a plurality of directionalcontrol valves in a hydraulic circuit for supplying a discharge pressurefluid from a single hydraulic pump through these directional controlvalves to the respective actuators so that all load pressure detectingpaths may be brought together and all the pressure compensation valvesmay be set with the highest load pressure, it can be seen that even ifany single actuator has taken its displacement end position so that thepump discharge pressure and the self-load pressure may be made equal toeach other, a load pressure within a said pressure detection path willbe made lower than the pump discharge pressure. Consequently, it can benoted that a pressure within the said second actuator of the pressurereduction portion in the pressure compensation valve for any otheractuator which has not yet reached its displacement end position will belower than the pump discharge pressure and since there will be noclosure of the said valve in the check valve portion of that pressurecompensation valve, the said any other actuator will be capable ofreceiving the pump discharge pressure fluid and hence may not bestopped.

In addition to the construction mentioned above, it is preferred that:

the said valve of the said check valve portion and the said spool of thesaid pressure reduction valve portion be arranged to be each slidableand are disposed coaxially in an opposing relationship with each otherin a valve body;

when the said valve has been slid towards the said spool by apreselected distance, the said inlet port and the said outlet port beadapted to communicate with each other;

the said spool be adapted to be slid under a pressure in the said firstpressure chamber in the said first direction away from the said valveand to be slid under a pressure in the said second pressure chamber inthe said second direction towards the said valve;

the said valve body be formed therein with a port that is connected to adischarge path of the said hydraulic pump; and

when the said spool has been slid by a given distance in the said firstdirection, the said internal passage in the said spool be adapted toallow the last mentioned port to communicate with the said secondchamber.

BRIEF EXPLANATION OF THE DRAWINGS

The present invention will better be understood from the followingdetailed description and the drawings attached hereto showing a certainillustrative embodiment of the present invention. In this connection, itshould be noted that such a embodiment as illustrated in theaccompanying drawings is intended in no way to limit the presentinvention, but to facilitate an explanation and understanding thereof.

In the accompanying drawings:

FIG. 1 is a cross sectional view illustrating a pressure compensationvalve in the prior art;

FIG. 2 is a circuit diagram of a hydraulic circuit using the pressurecompensation valve in the prior art; and

FIG. 3 is a a cross sectional view illustrating a pressure compensationvalve according to the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, a suitable embodiment of the present invention with respectto a pressure compensation valve will be set forth with reference to theaccompanying drawing hereof.

An explanation will now be given of a certain embodiment of the presentinvention with references to FIG. 3. The same components or members asin the prior art are designated by the same reference numerals.

As illustrated in FIG. 3, a valve body 31 is formed therein with a checkvalve bore 32 and a pressure reduction valve bore 33 which are disposedcoaxially in an opposing relationship with each other. The said checkvalve bore 32 is formed with an inlet port 34 and an outlet port 35. Thesaid check valve bore 32 has a valve 36 fittedly inserted slidablytherein and the said valve 36 is restrained with a plug 37 not to beslid leftwards from the position shown and thus constitutes a checkvalve portion 38.

The above mentioned pressure reduction valve bore 33 is formed with afirst port 40, a second port 41 and a third port 42. The said pressurereduction valve bore 33 has a spool 43 slidably fitted therein and isconfigured to have at its both sides, respectively, a first pressurechamber 44 that is opening to the said first port 40 and a secondpressure chamber 45 whose communication with the said third port 42 isestablished and blocked. The said spool 43 is adapted to be thrustedleftwards by a spring 47 that is provided between itself and a plug 46at the right hand side and, as a result, a pushing rod 48 integrallyformed with the spool 43 is allowed to project through a penetratingbore 49 to bring the above mentioned valve 36 into abutment on a plug37.

A load piston 51 is slidably inserted fittedly in a blind bore 50 thatis provided axially in the above mentioned spool 43, and a pressurereceiving chamber 52 is formed in an area closer to the bottom of thesaid blind bore 50. The said pressure receiving chamber 52 is designedto communicate via a radially extending, first bore 53 with a smalldiameter portion 54 of the said spool 43 and is thereby allowed tonormally communicate with the said second port 41. The above mentionedload piston 51 is formed axially with a fluid bore 55. The said fluidbore 55 is designed to normally communicate via a diametricallyextending, second bore 56 with the said second pressure chamber 45 andalso to be opening via a diametrically extending, third bore 57 and asmall diameter portion 58 to the peripheral surface of the said loadpiston 51. The said small diameter portion 58 is adapted to normallycommunicate with the said third bore 42 via a throttle 62 such as anarrow hole, a radially extending, fourth bore 59 and a second smalldiameter portion 60 which are formed of the said piston 43. And, in theinterior of the said spool 43, there is formed an internal passage 61that communicates the said second port 41 and the said second pressurereceiving chamber 45 with each other via the said first small diameterportion 54, the said first bore 53, the said pressure receiving chamber52, the said small diameter portion 58, the said third bore 57, the saidfluid bore 55 and the said second bore 56, when the said spool 43 hastaken a right hand side position against the resilient force of the saidspring 47. Further, the said internal passage 61 is designed tocommunicate via the said throttle 62 and the said fourth bore 59 withthe said third port 42. There is thus constituted a pressure reductionvalve portion 63.

An explanation will next be given with respect to the operation of theabove mentioned embodiment of the present invention.

If the said spool 43 from the position shown in FIG. 3 is thrustedrightwards under a self-load pressure P₁ within the said first pressurechamber 44 and its distance of displacement exceeds a value S, the saidpressure receiving chamber 52 will communicate with the said smalldiameter portion 58 of the load piston 51 and the said second port 41will communicate via the said internal passage 61 with the said secondpressure chamber 45. As a result, a pump discharge pressure P₀ will acton the above mentioned second pressure chamber 45 and the said spool 43will thereby perform a pressure reduction operation (an operation madewith the spool 43 allowed to slide leftwards to thrust the valve 36 inits blocking direction) and will eventually come to a halt at a positionat which the self-load pressure P₁ within the said first pressurechamber 44 and the pressure within the said second pressure chamber 45are made equal to each other.

The pressure fluid within the above mentioned second pressure chamber 45will be allowed to flow from the said second bore 56, the said fluidbore 55, the said third bore 57, the said throttle 62, the said fourthbore 59 and the said second small diameter portion 60 out into the saidthird port 42 and in turn into the load pressure detecting path 17.Then, since the said load pressure detecting path 17 is connected viathe throttle 25 to the reservoir 26, a constant flow will be created andalso a pressure difference will develop between behind and ahead of thesaid throttle 62, As a result, a load pressure P_(LS) will thereby bemade lower than the pressure within the said second pressure chamber 45.

This being the case, it can be seen that when an actuator has taken itsdisplacement end position to allow the load pressure P₁ and the pumpdischarge pressure P₀ to be made equal to each other and then thepressure within the said second pressure chamber 45 becomes the pumpdischarge pressure P₀, the load pressure P_(LS) that appears as anoutput at the said third port 42 will be lower than the pump dischargepressure P₀ by an amount that is commensurate with the diameter of thesaid throttle 62.

Accordingly, in case where the present embodiment is applied to ahydraulic circuit as shown in FIG. 2, it can be seen that even if anactuator has taken its displacement end position, with the load pressureP_(LS) within the said load pressure detecting path 17 made lower thanthe pump discharge pressure P₀ the pressure within the said secondpressure chamber 45 of the pressure reduction valve portion 63 in thepressure compensation valve that is connected to any other actuatorwhich has not yet reached its displacement end position will likewise bemade lower than the pump discharge pressure P₀. As a result, the saidvalve 36 under the pump discharge pressure P₀ at the said inlet port 34will be thrusted in its communicating direction to close neither thesaid inlet port 3 nor the said outlet port 35, thereby permitting thepump discharge pressure fluid to be fed to all the actuators.

Also, since the pressure difference between the pressure within thesecond pressure chamber 45 and load pressure P_(LS) can here be changedas desired by changing the diameter of the throttle 62, a pressurecompensation valve according to the present invention may be of anypressure compensation characteristic as optionally selected to enhancethe control performance of actuators.

While the present invention has hereinbefore been described with respectto certain illustrative embodiments thereof, it will readily beappreciated by a person skilled in the art to be obvious that manyalterations thereof, omissions therefrom and additions thereto can bemade without departing from the essence and the scope of the presentinvention. Accordingly, it should be understood that the presentinvention is not limited to the specific embodiments thereof set outabove, but includes all possible embodiments thereof that can be madewithin the scope with respect to the features specifically set forth inthe appended claims and encompasses all equivalents thereof.

What is claimed is:
 1. A pressure compensation valve, characterized inthat it comprises:a check valve portion having an inlet port that isconnected to a discharge path of a hydraulic pump, an outlet port thatis connected to an inlet side of a directional control valve and a valvefor controlling an area of opening between both said ports; and apressure reduction valve portion which is comprised of a spool thatdefines at its both sides a first pressure chamber and a second pressurechamber, respectively, and is adapted to be slidable to to allow saidvalve to be thrusted in a first direction in which said area of openingis increased under a self-load pressure applied to said first pressurechamber and to be slidable to allow said valve to be thrusted in asecond direction in which said area of opening is decreased under apressure within said second pressure chamber, an internal passage thatis formed inside of said spool and that is adapted to supply a dischargepressure fluid of said hydraulic pump to said second pressure chamberwhen said spool has been slid to assume not less than a predetermineddisplacement made in said first direction, a first throttle that isdisposed in said internal passage, and a port for establishing acommunication between a load pressure detecting path that is connectedvia a second throttle to a reservoir and said first throttle.
 2. Apressure compensation valve as set forth in claim 1, characterized inthat:said valve of said check valve portion and said spool of saidpressure reduction valve portion are arranged to be each slidable andare disposed coaxially in an opposing relationship with each other in avalve body; when said valve has been slid towards said spool by apreselected distance, said inlet port and said outlet port are adaptedto communicate with each other; said spool is adapted to be slid under apressure in said first pressure chamber in said first direction awayfrom said valve and to be slid under a pressure in said second pressurechamber in said second direction towards said valve; said valve body isformed therein with a port that is connected to a discharge path of saidhydraulic pump; and when said spool has been slid by a given distance insaid first direction, said internal passage in said spool is adapted toallow the last mentioned port to communicate with said second chamber.